1. Field of the Invention
The present invention relates to a hydraulic control system for a vehicle automatic transmission, whereby locking of a brake, which is a reacting element, can be prevented during the shift operation between a second speed to a fourth speed and responsiveness of the shift operation is improved.
2. Description of Related Art
In general, an automatic transmission provides a necessary gear ratio to operate the vehicle under a wide range of speeds and loads. It does this with a minimum amount of effort on the part of the driver. That is, automatic upshifts and downshifts are a convenience for the driver because a foot-operated clutch is not required to shift gears, and because the vehicle can be brought to a stop without the use of a clutch and without shifting the transmission into neutral.
A conventional automatic transmission for a vehicle comprises a torque converter having an impeller, a turbine and a stator, a gear train connected to the torque converter to provide various forward speed ranges and reverse, a plurality of friction members such as disc clutches, one-way clutches which control gear action, and a hydraulic control system for controlling the operation of the friction members.
The gear train is selectively operated by applying each friction member as an input element, an output element or a reacting element. The application or release of each friction member is performed in order.
However, if one friction member is applied before another previously-applied friction member is released, the gear train may be damaged.
In addition, the gear train generally used a one-way clutch for reacting force of a rotating member. The use of the one-way clutch makes the gear train complicated.